Lead perchloric acid primary cell



Dec- 27 1949 J. c. wHlTE ErAL LEAD PERQHLORIC ACID PRIMARY CELL FiledJan. i9, 1943 30 -My w14/ 2-/6 arb .S www. w mnluhw. WAP fw C.BJ.H MrWHWN ENAWW wwm JJEW PATENT OFFICE 2,492,206 LEAD PERCHLORIC ACID PRIMARYCELL Joseph C. White, University Park, Md., John H. Baldwin and EdwardJ. Peebles, Washington, D. C., and Wilson H. Power, Greenbelt, Md.

Application January l9, 1943, Serial No. 472,830

1 Claim.

(Granted under the act of March 3,` 1883, as amended April 30, 1928; 3700. G. 757) 'This invention relates to electric batteries, and it isparticularly concerned with the manufacture of a primary cell capable ofhigh current output at low temperatures.

The most commonly used heavy duty battery is the usual sulfuricacid-lead storage cell. Cells of this type, as well as various primarycells, have been made which produce high currents for considerableperiods of time, and they are capable of producing extremely highcurrents for short periods, known as flash currents. It is this abilityto furnish flash currents of high intensity (and high power due to lowinternal resistance) which has permitted the use of battery power formoving or operating fairly large engines, such as starting a gasolineengine and various mechanisms of ordnance.

However, these cells or batteries are not nearly so useful at very lowtemperatures, and sustained flash currents cause the available voltageto drop sharply. Also they are quite heavy in relation to the currentoutput available. The drop in available current is particularlynoticeable at temperatures below about C., and the current output at,say, 40 C. is usually of the order of a few percent of the roomtemperature maximum. A new type of cell has recently been developed foroperation at low temperatures such as are encountered in the use ofradio-sonde apparatus. This cell is very light weight and compact, andits output at room temperature is more than that of similar cells now onthe market. It is characterized by the relatively slight drop in outputat temperatures as low as -40'C., and

a really useful output at temperatures as low.

as 60 C., where commercial cells cease to function. Like the sulfuricacid storage cells this cell has a lead negative plate and a leaddioxide positive plate, but it differs from conven-v tional cells inemploying aqueous perchloric acid as the electrolyte. This cell isdescribed and claimed in the Schrodt and Craig application, Serial No.424,160, filed December 23, 1941. As described therein, the lead dioxideis supported by a noble metal such as gold, platinum or tantalum, andpalladium is preferred. The reason for not using a lead support for thelead dioxide as is done in sulfuric acid batteries is because thedioxide layer is porous and the perchloric acid attacks the metalunderneath.

This invention is concerned, not with the small, light weight cellssuitable for radio-sonde equipment, but with batteries capable ofextremely high, sustained flash currents, even at low temperatures; thatis, batteries which will deliver a relatively enormous amount of powerfor a short period of time under almost any conditions. In this respectthe invention is a modification of the radio-sonde type of batterydisclosed in the Schrodt and Craig application referred to above.

. Without excessive loss of voltage.

Accordingly, this invention provides a battery of the perchloricacid-lead type which is characterized by its lightness and smaller sinewhen compared to the standard sulfuric acid-lead cells of equivalentpower, and is capable of delivering exceedingly high currents at lowtemperatures The invention also contemplates specially designed positiveand negative plates, or electrodes, which may be made cheaply by themethod herein disclosed, and combinations of positive and negativeplates which are especially adapted to the production of higher cellvoltages and currents under adverse operating conditions.

The battery, or cell, of this invention utilizes perchloric acid as theelectrolyte and lead dioxide as the positive electrode, and the negativeelectrode comprises one or more metals selected from the groupconsisting of magnesium, aluminum, manganese, zinc, iron, cadmium, tinand lead. The electrode need not be the pure metal, and in fact alloysof these metals with various other metals are useful, depending on theparticular use for which the cell is designed. Particularly useful forhigh flash currents with sustained voltages is a negative electrodecomprising an aluminum grid coated with lead, as hereinafter described.

In order to obtain a high capacity cell itis necessary to constructfairly thick electrodes of large surface area. It is prohibitive to makesuch electrodes of noble metals, so that the lead dioxide must besupported on some other conducting material, such as carbon or certainmetals, on which it can be deposited in an adherent condition and whichis not attacked appreciably by the constituents of the cell.

Very few metals other than the noble metals do not produce strongcouples with lead dioxide in perchloric acid solution. On suchrelatively inactive metals, or alloys as nickel, chromium, stainlesssteel, cobalt, or iron, or on carbon, however, the lead dioxide can bedeposited in a strong, dense, adherent layer which will not decomposerapidly in contact with perchloric acid solution. However, metals whichproduce strong couples can be used as grid materials for the positiveplate ifiirst plated with a relatively inactive metal such as nickel orcobalt. Perforated copper or aluminum sheet, or wire screen, plated withnickel, are preferred as supports for the lead dioxide.

The layer' of lead dioxide may be obtained on the nickel surface inseveral ways, but the most practical method comprises electrodepositingthe lead dioxide on the nickel from a lead nitrate bath. However, it isnecessary to control the pH of the bath within rather narrow limits if adense, adherent layer is to be obtained on the nickel. In general the pHshould be maintained 3 within the range of about to 2, and this is mosteasily accomplished by circulating the lead nitrate solution (containingnitric acid formed by the electrolysis) through a lter bed of lead oxideor carbonate, or other basic lead com.- pound, and returning the ltrate,enriched with lead, to the plating bath.

In order that the invention mayT be clearly understood typicalembodiments thereof are de scribed with reference to the accompanyingdrawing, in which:

Fig. 1 is a cross-sectional vieu.r of a complete cell made in accordancewith the invention;

Fig. 2 is a cross-sectional view of one form of positive electrode foruse in the cell of" Fig. l;

Fig. 3 is a cross-sectional view of a negative electrode which may beused in the battery of Fig. 1; and

Fig. 4 is a schematic diagram of the method of preparing the positiveelectrode.

Referring to Fig. 1, the cell comprises a container III of glass orsynthetic resin partially filled with aqueous perchloric acid II inwhich are immersed negative electrodes I2 and positive electrodes I3,supported in position by a brace I4. A vent I5 is provided to permit theescape of gas. The negative electrodes I2 may be any of the metals oralloys mentioned above, and .they may be of any shape desired,preferably not too thin because they are consumed during use. Thepositive electrodes I3 comprise a conductive support (e. g. metal orcarbon), nickel plated, and bearing a coating of lead dioxide.

'Ihe preferred design of positive plate is shown in Fig. 2 in which acopper or aluminum wire screen grid is soldered, clamped or otherwisefastened to a metal holder 2|. The screen 20 bears a thin coating ofnickel or cobalt, which may be advantageously electrodeposited accordingto standard practice, preferably from a nickel or cobalt sulfate bath orother solution which will give a vbright deposit. The nickel platedscreen 20 carries a dense, firmly adherent layer of lead dioxide 22. Thelead dioxide layer 22 is prepared on the screen 2l) by electrolysis oflead nitrate, asv

described in connection with Fig. 4. If desired a carbon grid may beused in place of the copper or aluminum, in which case the nickelplating may be omitted and the lead dioxide deposited directly" l on thecarbon.

In Fig. 3 is shown a cross-sectional view of one form of negativeelectrode which is useful inthe battery of this invention where it isdesirable to maintain the highest possible voltage toward the end of thedischarge, at very high currents. This is accomplished by presenting aless active metal to the electrolyte during the rst part of thedischarge, at which time the electrolyte is strongest, and then exposinga more active metal toward the end of the discharge. In this way it ispossible to utilize the high voltage obtainable from a metal so activethat it would readily dissolve in the pei'- chloric acid by displacementof hydrogen, without excessive loss of metal in this manner. In thefigure, a. perforated sheet or grid (which may equally well be a wirescreen) is fastened to a metal holder 3|, in the same manner that thegrid 20 is fastened to the holder 2l in Fig. 2. The grid 3II is made ofone ofY the more active metals in the group of metals indicated above assuitable negative electrode material, such as magnesium or aluminum, andit is plated or otherwise coated with a less active metal 32, such asiron or lead. During discharge of the battery the less active metal 32is consumed until, toward the end of the discharge, the grid 30 becomesexposed to the electrolyte at various points, such as at 33, and

the cell voltage is sustained or even raised. This may be due, in part,to thev higher potential be 5 tween the positive electrode and the moreactive metal, and it may be due in part to the displacement of some ofthe already dissolved, less active metal from the electrolyte, but theprecise mechanism of the reaction which takes place and sustains thecell voltage is not known. The important fact is that the cell voltage,and hence power output, may be sustained or even increased by thismethod where extremely high currents are demanded for a relatively shortperiod of time.

Referring to Fig. 4, the nickel plated screen 20, of Fig. 2, is immersedin an aqueous solution of lead nitrate 4D in a container 4 I, and thescreen 20 is connected to the positive side of a source of directcurrent. Also immersed, in the solution are two electrodes 42, which maybe made of copper, carbon, or other conductive material. Theseelectrodes are connected to the negative side of the source of directcurrent. On flow of current through the solution 4D, metallic lead isdeposited on the electrodes 42 and lead dioxide is deposited on thescreen 2li. `As the solution 40 becomes depleted of lead, the hydrogenion concentration, or acidity, rises, due to formation of nitric acid.If the acidity rises very much the lead dioxide deposit will not beadherent.` Therefore the solution 40, along with spongy lead droppingsfrom the electrodes 42, is drawn from the bottom of the container 4Ithrough a conduit 43, controlled by a valve 44, to a pump 45. The pump45 lifts the solutionID through a conduit 46 into a container 41 havinga porous bottom 48 covered by a thick layer of an insoluble basic leadsalt 49, such as lead oxide or lead carbonate. The solution 40 filtersthrough the layer 49, leaving the spongy lead droppings, and the nitricacid in the solution 48 reacts with the lead salt to form more leadnitrate. From the layer 4'9 the lead-enriched solution 4D, of lowacidity, returns through a conduit 50 to the container 4I for furtheruse. In practice it has been found that the solution 40 may be reusedfor an almost unlimited time, when regenerated as above described, thusindicating that the decomposition of the nitric acid to oxides ofnitrogen is extremely small. However, there is some lead nitrate lossfrom adherence to plates removed from the bath, known as drag out," andthis is replaced by periodical additions of lead nitrate to the bath.

The concentration of lead nitrate in the solution 40 is not critical,excellent results being obtained with a concentration of about 200 to500 grams per liter, preferably about 275 grams per liter, with no freenitric acid added. Sometimes trouble is encountered with lead treeingfrom the electrodes 42. This can be prevented by adding a small amountof a copper salt to the solution 40, but after operation has beenstarted the copper salt is not necessary, apparently due to solution ofa small amount of nickel from the screen 20. The current density is notcritical in depositing the lead dioxide, but the densest and strongestdeposit is obtained with a current density within the range of about 30to about 300 am peres per square foot, with 65 to 125 amperes peisquarefoot preferred. The temperature of the bath will rise during operation,but a good deposit is obtained anywhere from room temperature to about60 C. However, high temperatures should be avoided to prevent crackingof the brits f tle lead dioxide coating after coming to roomtemperature.

The following examples illustrate typical results obtained with variouscombinations of electrodes according to the invention.

seance tion is less. Extremely weak acid is undesirable because itobviouslyv will not provide a vigorous cell reaction. For generaloperation and especially very -low temperature operation, aconcentration of about 50% is generally preferable because at thisconcentration the freezing point is On placing the positive and negativeplates in a 40% aqueous solution of perchloric acid the cell wasdischarged at a .constant rate of 85 amperes for a period of sevenminutes. During the discharge the voltage dropped from 1.36 to 1.32

. volts.

Although the voltage obtained with an iron negative pole is lower thanthat obtained with some other metals it is remarkablyrconstant at such ahigh rate of discharge. l

Example 2 A l6-mesh copper wire screen was cadmium plated to provide twonegative. plates (i. e. one

pole) having a total area of about 186 square inches. The positive poleof this cell was identical to the one described in Example 1, and the.

concentration of perchloric acid was also the same.

When this cell was discharged ata current of t 85 amperes for sevenminutes the voltage dropped from 1.72 to 1.40 volts.

Example 3 A perforated aluminum sheet was plated with a thin coat ofnickel and then plated with a heavy deposit of lead dioxide in themanner described with reference to Fig. 4. This plate was used as thepositive pole of the cell and had a total area of about 45 squareinches... Two sheets of lead were placed in the cell on either side ofthe positive pole and connected together toform a negative pole with atotal area of about 69 square inches.

This cell was discharged at a constant current oi' 50 amperes for 9minutes, during which time the voltage dropped from 1.70 to 1.42 volts.

Example l A perforated aluminum sheet. nickel plated. was used as thesupport for the lead dioxide which was deposited in the manner describedwith referencetol'ig. 4. A

The negative plates were two similar perforated aluminum plates whichhad been sprayed with lead. v

lowest and conductivity highest. Also for very low temperature operationmagnesium may he used to advantage in the construction of the negativepole, whereas it is somewhat too active for practical use at roomtemperatures.

Where weight is a primary consideration both electrodes may be made ofaluminum, nickel coated for support ofthe lead dioxide to form thepositive pole, and with one of the less active y metals indicated forthe negative pole. As with magnesium, aluminum alone may beadvantageously used as the negative pole for low temperature work,although it is also useful at room temperatures, particularly where itbears a starting coat of a.' less active metal.

Other advantageous combinations of metals for the negative electrode arealuminum or magl nesium coated with cadmium or iron, and zinc Both poleshad areas of about 42 square inches.

When this cell was discharged, using perchloric acid electrolyte.4 at aconstant current of 85 amperes. the initial potential of 1.59 voltsdropped slowly to 1.34 in four minutes and then rose to 1.58 volts inthe next three minutes.

The concentration of perchloric acid in the cell is not critical. Forpractical reasons it is not deairable to exceed about 71%. as at thisconcentration the perchloric acid forms-fan azeotropic mixture withwater and also the degree of ionizacoated with cadmium, tin or lead." l

Many variations will be apparent to those skilled in the art and theinvention should not be 4limited other than as deilned by the appendedclaim.

The invention described herein may be manufactured andr used by or forthe Government of the United States of America for governmental purposeswithout the vpayment of thereon or therefor.

A primary cell characterized by its high ash current and eiciency at lowtemperature comprising a positive electrode consisting of a cobaltcoatedaluminum support bearing a coating of lead dioxide. an electrolyteconsisting of a solution of perchloric acid and a negative electrodeconsisting of aluminum coated with lead.

JOSEPH C. WHITE. .JOHN H. EDWARD J. PEEBLES.

WILSON H. POWER..

Y REFERENCES crrnn The following references are of ree-.m1n .ne

file of this patent:

UNITED STATES PATENTS Number Name Date 368,190 Case Aug. 16, 1887396,769 Sellon Jan. 29, 1889 408,367 Aldrich Aug. 6, 1889 441,959Kennedy Dec. 2, 1890 759,065 Betts ---..--i May 3, 1904 773,961 MorganNov. l', 1904 900,502 Ferchland et al. Oct. 6, 1908 1,425,163 Bardt Aug.8, 1922 1,826,724 Booss et al Oct. 13, 1931 FOREIGN PATENTS NumberCountry Date 18,036 Great Britain 1895 456,082 Great Britain Nov. 3,1936 OTHER. REFERENCES Vinal, G. W.: Storage Batteries. 2nd ed. (1930),page1-i8.

Schrodt et al.: N. B. S. Battery for Low Temperature Operation, P. B.27276 (O. S. R. D. 558). pages 2 to 6. Report dated Aug. 18. 1941.

any royalties

